The purpose of the 'Manifests' tab is if you want a copy of everything you shipped, however, it is not required by any of the carriers Skipjack does business with.
An instance when this could be useful would be if a hazardous material was being shipped because the government and FedEx have to know they have this material on their vehicles. In this case, you would enter the date and time, and then the manifest will appear. Hovering over it will present the options to 'View Hazmat' or 'View Manifest'.
View Hazmat: Clicking this will generate and open a pdf of the hazmat of the shipment. This pdf will contain all of the details about the hazmat. If you have hazmat, you'll want to close the manifest by the end of the day and give the hazmat documentation to the carrier.